Spectroscopic light source



Nov. 16, 1965 G. BOLDT 3,218,514

SPECTROSCOPIG LIGHT SOURCE Filed July 5, 1962 vz' 1b 3f a a i l 6 "4 i 5 w n i 5 7 gg@ f J/ w// ////A 7m/enfer:

GNTHER amm' United States Patent Office 3,218,514 Patented Nov.. 16, 1965 3,218,514 SPECTRGSCOPIC LIGHT SOURCE Gnther Boldt, Munich, Germany, assignor to Max- Planck-Gesellschaft zur Frderung der Wissenschaften e.V., Gottingeu, Germany Filed July 5, 1962, Ser. No. 207,505 Claims priority, application Germany, July 11, 1961, M 49,633 8 Claims. (Cl. 315-236) The invention relates to a spectroscopic light source for the vacuum ultraviolet.

Vacuum-spectroscopic spark chambers according to Siegbahn have been generally used in the past as spectroscopic light sources for the vacuum ultraviolet. In these spark chambers, the distance between the electrodes amounts to about 1 to 2 mm., a capacitor of about 1.03 to 1.3 pf. is connected in parallel to the spark gap, and the spark voltage amounts to about 70 kv.

It is also known to use so called slide-spark gaps as light sources for the vacuum ultraviolet. Slide-spark gaps require, however, similar high operating voltages as the irst mentioned Vacuum spark chambers.

In practice, the high operational voltages of the known arrangements have proved to be extremely inconvenient. Moreover, the intensity of the known light sources is not very satisfactory. The danger of handling the high voltages and the required long exposure times have prevented in many cases the use of the known light sources.

It is therefore the object of the invention to provide a spectroscopic light source for the vacuum ultraviolet which only requires moderate operational voltages, yet exhibits a substantially higher intensity than the known light sources of this kind.

A spectroscopic light source for the vacuum ultraviolet comprising two spark electrodes which are arranged in a vacuum chamber and are adapted to be connected to a capacitor that supplies the spark energy, is characterised according to the invention by a movable ignition electrode which is arranged close to one of the spark electrodes, and which can be deflected so far, that it can contact the adjacent spark electrode, and by a capacitor which can be connected between the ignition electrode and to the spark electrode adjacent to the former.

The operating voltages of the capacitors are of an order to magnitude of about 1 kv. The capacity of the capacitor that is connected to the ignition electrode is so selected that as soon as the adjacent main electrode is contacted a strong discharge plasma is formed which initiates the discharge between the spark electrodes. The capacitor, which is connected by a low-inductance connection to the spark electrodes, then discharge with a steeply rising short current pulse so that a highly ionised plasma is set up between the main electrodes which plasma supplies the desired short wave radiation of high intensity.

A constructional example of the invention is represented in the drawing.

Two coaxial electrode arrangements are inserted vacuum tightly and electrically insulated into a vacuum chamber 1 which consists of metal and which can be connected by means of suitable flanges 1a, 1b to the inlet gap of a spectrographic apparatus, monochromator or the like, not shown, and if desired to a pump, likewise not shown. The electrode arrangements consists of metal holders 2, 3 which are hollow and adapted to be cooled by flowing cooling water, as indicated by arrows. The electrode holders carry at the sides which face another the actual electrodes 4, 5 which preferably consist of carbon. The electrodes have substantially the shape of a truncated cone, they are provided with an axial bore, and they have a cone-shaped recess at the end faces which face one another. Insulating cylinders 6, 7 of porcelain or ceramic material are arranged between the electrode arrangements and their cavities in the vacuum chamber 1. The electrode arrangements are sealed by means of annular seal of rubber of the like which are not designated by a reference numeral.

A pin shaped ignition electrode 8 extends into the bore of the one electrode 4 and is fastened to one end of a long steel needle 9. The steel needle 9 is arranged within a tubular extension 10 which is arranged coaxially with the electrode arrangements and forms an extension of the central opening of the electrode holder 2. The end of the steel needle 9 remote from the electrode pin 8 is fastened to the head 11 of the extension 10. The extension 10 consists of a non-magnetic material so that it is possi-` ble to deliect the steel needle 9 by means of an electro-4 magnet 12 arranged outside of the tubular extension 10.

the detlection of the steel needle 9.

A capacitor 13 or a battery of capacitors is connected` through a low-inductance connection to the electrode holders 2, 3. A second capacitor 14 is connectedl between the electrode arrangement 2, 4 which includes the ignition pin 8 and the support 10, 11 which is conductively connected to the steel needle 9 that carries the electrode 8.

The capacitor 13 connected to the main electrodes 4, 5 may have a capacity of about 1000 pf. and an operational Voltage of about 1 kv. The capacitor which is connected to the ignition electrode has a capacity of about 2 pf. and an operational voltage of about 1 to 1.2 kV. Both capacitor arrangements are connected through suitable loading resistors 15 or 16 respectively preferably to the same current source 17 adapted to be connected to the mains. The time constant of the loading circuit is selected in accordance with the spark frequency which can be determined by means of a suitable control device.

In operation, the magnet 12 is energized intermittently in the rhythm of the spark frequency means of a time switch or the like so that the steel needle 9 is caused to oscillate and the carbon pin 8 to contact the wall of the bore in the electrode 4. As soon as a contact between these two electrodes takes place, the ignition capacitor 14 discharges and an ignition plasma is produced within the bore of the electrode 4 and in its cone shaped recess which plasma is suiciently ionised and extended to initiate immediately the main discharge between the electrodes 4 and 5. Between the main electrodes 4, 5 then ows from the capacitor battery 13 a comparatively short current pulse of high intensity (measurings have shown that the currents are of an order to magnitude of about 20 ka.) whereby a highly ionised plasma is set up between the electrodes 4, 5 which supplies a highly intensive line radiation extending below A. The radiation includes for instance lines of CIV, OVI and SiV (from the porcelain insulators). By the use of normal Schumann plates sufcient lines `are obtained, even with an exposure time of only two minutes, to be able to effect adjustments and wave length calibrations within the range of interest.

The continuous radiation emitted from the electrodes 4, 5 as such is obscured by the insulating cylinders 6, 7. Since carbon electrodes do not sputter as metal electrodes do, the portion of the plasma in the annular gap between the insulating cylinders 6 and 7 which is visible through the inlet gap of the spectrographic apparatus, is free from glowing solid particles so that a clear line spectrum without background is obtained.

What we claim is:

1. A vacuum spark discharge lamp device comprising, in combination:

(a) a vacuum chamber;

(b) two spaced spark electrodes disposed n said vacuum chamber;

(c) rst capacitor means connected between the spark electrodes for supplying spark energy;

(d) ignition electrode means adjacent one of said spark electrodes and mounted for movement to contact the, adjacent electrode;

(e) second capacitor means connected between said one spark electrode and said ignition electrode means for` supplying ignition energy; and

(f) means for causing the movable electrode means to contact said `one spark electrode thereby to discharge said second capacitor means.

2. A device as defined in claim 1 wherein the adjacent spark electrode has a central bore and the movable ignition electrode includes a pin electrode arranged within the central bore of the spark electrode.

3. A device as defined in claim 2 wherein the movable ignition electrode means further includes a steel needle to which the movable ignition electrode is fastened and wherein said means for causing contact includes magnet means for detiectng said steel needle and causing said ignition electrode to contact the adjacent spark electrode.

4. A device as dened in claim 3, wherein an A.C. source is connected to energize said magnet means, and

said steel needle being tuned to the magnetic eld produced by said magnet means.

5. A device as defined in claim 1, wherein the end faces of the spark electrodes which face one another are each provided with a cone-like recess.

6. A device as defined in claim 1 comprising screening means arranged for obscuring the direct radiation from the spark electrodes.

7. A device as dened in claim 1 wherein the spark electrode and the ignition electrode are of carbon.

8. A device as dened in claim 1 comprising watercooled electrode holders carrying the electrodes, and annular insulating cylinders surrounding the holders and projecting to some extent beyond the effective ends of the electrodes.

References Cited by the Examiner UNITED STATES PATENTS 1,555,893 10/1925 Thompson 317-147 2,441,822 5/ 1948 Klemperer 320-1 2,607,024 8/ 1952 Marwell et al. 315--331 2,643,574 6/1953 Todd 315-237 2,703,374 3/ 1955 Fruenagel. 3,087,092 4/1963 Laierty 315-330 JOHN W. HUCKERT, Primary Examiner.

DAVID I. GALVIN, JAMES D. KALLAM, Examiners. 

1. A VACUUM SPARK DISCHARGE LAMP DEVICE COMPRISING, IN COMBINATION: (A) A VACUUM CHAMBER; (B) TWO SPACED SPARK ELECTRODES DISPOSED IN SAID VACUUM CHAMBER; (C) FIRST CAPACITOR MEANS CONNECTED BETWEEN THE SPARK ELECTRODES FOR SUPPLYING SPARK ENERGY; (D) IGNITION ELECTRODE MEANS ADJACENT ONE OF SAID SPARK ELECTRODES AND MOUNTED FOR MOVEMENT TO CONTACT THE ADJACENT ELECTRODE; (E) SECOND CAPACITOR MEANS CONNECTED BETWEEN SAID ONE SPARK ELECTRODE AND SAID IGNITION ELECTRODE MEANS FOR SUPPLYING IGNITION ENERGY; AND (F) MEANS FOR CAUSING THE MOVABLE ELECTRODE MEANS TO CONTACT SAID ONE SPARK ELECTRODE THEREBY TO DISCHARGE SAID SECOND CAPACITOR MEANS. 